1. Field of the Invention
The present invention relates to a method for manufacturing a pressure container used for a high pressure combustion pipe of a rocket propulsion motor and having a cylindrical shape with opposite dome ends, and more particularly to a method for manufacturing a pressure container having opposite dome ends with different opening diameters using polar winding and helical winding processes.
2. Description of the Prior Art
Generally, various high pressure containers and pipes requiring a light weight and a resistance to a high pressure are made of composite materials of resins and fibers of a high strength, such as fiber-reinforced plastic materials. As typical methods for manufacturing pressure containers using such composite materials, there have been known a helical winding process and a polar winding process in which a composite band made by impregnating fi laments such as glass fibers or carbon fibers in a thermosetting resin of liquid phase is wound continuously on the surface of a mandrel having a certain shade.
First, the procedure for manufacturing a pressure container using the helical winding process will be described in conjunction with FIGS. 1A and 1B.
As shown in FIGS. 1A and 1B, a mandrel 1 is prepared which has a certain shape having opposite dome ends provided with metal bosses 3 and 4. The metal bosses 3 and 4 have diameters d1 and d2, respectively. In accordance with the helical winding process, a winding band 2 which comprises a plurality of fibers impregnated in a resin material is wound helically on the outer surface of the mandrel at a certain winding angle. Where the diameter of mandrel is D and both the diameters d1 and d2 of bosses 3 and 4 are d, the winding angle a is expressed by the following equation: ##EQU1## At the winding angle based on the equation (1), the winding band 2 is subjected to a tension when it is wound around the mandrel 1. Accordingly, the winding band 2 is maintained at a straight line state between two optional points on the mandrel 1, as shown in FIG. 1B. The winding path of the winding band 2 at opposite dome ends of the mandrel 1 is always maintained tangentially to the peripheries of bosses 3 and 4 so that it extends in perpendicular to the radial direction of bosses 3 and 4.
On the other hand, where the diameter of a pressure container to be manufactured is constant, the winding angle .alpha. is increased in proportion to the size of openings at the dome ends of pressure container, as apparent from the equation (1).
In case that the openings formed at opposite dome ends of the pressure container are identical or similar to each other in size, the winding angles at the opposite dome ends are identical to each other, so that the winding band maintains a straight winding path between two optional points thereon. Thus, there is no difficulty in applying the helical winding process for manufacturing the pressure container. Where the diameters of openings at opposite dome ends of the pressure container are different from each other, however, the following problems occur.
That is, where the openings of opposite dome ends are different from each other in size and when a winding band is wound on a mandrel at a small winding angle with respect to the dome end having the smaller opening, to extend in perpendicular to the radial direction of the boss at the same dome end, the winding band is confined at the boss having the larger diameter, even though the winding path at the dome end having the larger opening tends to be maintained at a small winding angle, in similar to the winding path at the dome end having the smaller opening. Under the condition, a slippage of the winding band is caused by the tension which is applied to the winding band. Such a slippage causes the winding path to extend tangentially with respect to the boss having the larger diameter and thus have a large winding angle.
As a result, winding band turns which have been wound on the mandrel at a low winding angle become slip, so that the winding angles thereof are varied from the small winding angle at the dome end having the smaller opening to the large winding angle at the dome end having the larger opening. Consequently, the winding band path does not form a straight line, but a curved line between two optional points on the surface of mandrel.
On the other hand, when a winding band is wound on a mandrel at a large winding angle with respect to the dome end having the larger opening, to extend in perpendicular to the redial direction of the boss at the same dome end, and if assuming that there is no slippage of the winding band at the opposite boss having the smaller diameter, the winding band path at the dome end having the smaller boss extends in perpendicular to the radial direction of the smaller boss at a position spaced apart from the smaller boss a certain distance. As a result, the boss has a portion on which the winding band is not wound, thereby resulting in poor pressure containers.
If outward slippage of the winding band occurs around the smaller boss, the winding band is departed from the surface of mandrel, thereby causing the helical winding to be impossible. Otherwise, inward slippage of the winding band causes the winding band to come into contact with the outer peripheral surface of the smaller boss. At this time, the winding band is wound along a winding path perpendicular to the radial direction of the smaller boss and at a small winding angle, due to the tension applied to the winding band. As a result, the overall winding angles are varied from the small winding angle at the dome end having the smaller opening to the large winding angle at the dome end having the larger opening. Consequently, the winding band path forms a curved line between two optional points on the surface of mandrel. The curvature of winding band path increases as the difference in diameter between dome end openings of the pressure container to be manufacture increases. When the winding band is not wound along a straight path of the minimum length, but a curved path, the fibers of winding band can not exhibit sufficient effects, thereby causing the pressure resistance characteristic to decrease. As a result, the pressure container itself can not resist to the internal pressure and thereby is broken.
Now, the procedure for manufacturing a pressure container using the polar winding process will be described in conjunction with FIG. 2.
As shown in FIG. 2, a mandrel is prepared which has a certain shape having opposite dome ends provided with metal bosses 3 and 4. The metal bosses 3 and 4 have diameters d1 and d2, respectively. In accordance with the polar winding process, a winding band 2 which comprises a plurality of fibers impregnated in a resin material is wound along straight paths between opposite bosses 3 and 4 on the outer surface of the mandrel 1 at a certain winding angle. Where the length of mandrel is L, the winding angle op is expressed by the following equation: ##EQU2## For preventing the slippage of winding band on the surface of mandrel when a tension is applied to the winding band between two optional points in the winding band path based on the polar winding, the winding band path should form a straight line of the minimum length and be perpendicular to the curved surface of mandrel. In this connection, the winding angle capable of preventing the slippage of winding band corresponds to .alpha. of the equation (1) at given dome opening sizes.
Where a pressure container having d1 of 88 mm, d2 of 250 mm, D (the diameter of mandrel) of 353 mm and L of 1,000 mm is manufactured using the polar winding process, the winding angle becomes 9.6.degree. according to the equation (2). On the other hand, the winding angles capable of preventing the slippage of winding band at opposite domes are 14.4.degree. and 45.0.degree., respectively, according to the equation (1). However, 9.6.degree. which is the winding angle for polar winding is considerably different from 45.0.degree. which is the winding angle capable of preventing the slippage of winding band at the larger boss. As a result, when the pressure container shown in FIG. 2 is manufactured using the polar winding process, the winding band slips outwardly at the larger boss, thereby causing the polar winding to be impossible.
Specifically, the fibers tends to be wound at the anti-slippage angle at the larger boss. This tendency make it impossible to apply the polar winding process for manufacturing the pressure container shown in FIG. 2, since the fibers move outwardly away from the surface of mandrel, due to the considerable angle difference between the anti-slippage winding angle .alpha. and the polar winding angle .alpha..sub.p, that is, +35.4.degree..
Accordingly, there is a problem in applying either of the helical winding process and the polar winding process for manufacturing a pressure container having opposite dome end openings with considerably different sizes.